Oral communication is a vital element in education, employment, social functioning and self-expression. At least 89% of the nearly seven million individuals diagnosed with idiopathic Parkinson disease (IPD) worldwide have a speech or voice disorder, yet only 3-4% receive speech treatment. Over the past fifteen years, our research has generated the first efficacy data for speech treatment for people with IPD. This treatment, called LSVT/LOUD, trains increased movement amplitude of respiratory-laryngeal systems by stimulating vocal loudness, while re-training the sensory motor processes involved in disordered speech communication. Treatment effects extend beyond the respiratory-laryngeal focus to include improvements in articulation, facial expression, swallowing and communicative gestures. Furthermore, treatment results in long lasting improvements (out to 2 years) that are correlated with brain re-organization as revealed by recent neural imaging studies. These findings are consistent with advances in neuroscience that have demonstrated activity-dependent neural plasticity associated with intensive exercise in animal models of PD and in humans with stroke-related hemiparesis. Collectively these data challenge the long-standing assumptions in the rehabilitation community that there is no potential for behavioral or neural recovery in people with IPD. We propose to continue to develop and refine our treatment model by seeking to understand the neural bases of recovery of function in IPD. The question addressed in this proposed funding cycle is whether there is something fundamental about the specific training target of vocal loudness that taps into key elements of successful speech rehabilitation in IPD. We propose to address this question by comparing LSVT/LOUD (which targets respiratory-laryngeal movements) with a contrastive treatment, ENUNCIATE (which targets orofacial-articulatory movements). We will compare these two treatments with different training targets, but matched on training modes in terms of their differential impact on neural reorganization, behavioral outcomes, and long-term maintenance. Such information is crucial for the advancement of our treatment protocols and will provide a behavioral and neural foundation for understanding mechanisms of successful speech rehabilitation. Improving communication in people with IPD can have a positive impact on quality of life and prevent social isolation. Virtually every individual with idiopathic Parkinson disease (IPD) will have problems related to communication that may diminish their quality of life and result in isolation from family and friends. Our efficacious speech treatment for people with IPD (LSVT/LOUD) has been shown to improve communication for as long as two years and improve the function of the brain. The proposed studies will advance our knowledge of the behavioral and neural mechanisms underlying improved speech communication and offer insight into the neural bases of recovery of function in Parkinson disease.